Test used by the British Secret Service to test observation skills...

I probably stopped trying way to soon, but the tests assume a good (prior) knowledge of London, right?

The observation test is the most interesting one - you don't need any knowledge of London to do it. The map reading etc is a bit more problematic...

I got full marks on the map reading one, but I do know the area around Waterloo and London Bridge pretty well.

....does noticing the "try a flash free test" link scores as a win, or it was a bug?

Test used by the British Secret Service to test observation skills... (mi5.gov.uk)